This invention is related to bicycle computers and, more particularly, to a speed sensor that is integrated into a motor unit used to shift a bicycle transmission.
Bicycle computers are often used to measure, calculate and display various riding parameters such as bicycle speed, distance traveled, pedaling speed, etc. Such computers usually include a display that is mounted to the handlebar and at least one sensor assembly mounted to the front or rear wheel. The sensor assembly usually includes a magnet that is mounted to one of the wheel spokes and a magnetic sensor that is mounted to the bicycle frame such that the magnet passes in close proximity to the sensor as the wheel rotates. The magnetic sensor is connected to a wire which, in turn, is routed along the bicycle frame to the display.
One problem with known bicycle computers is that the magnetic sensor is mounted to a small diameter portion of the frame, such as a steering fork tube or a rear chainsaw, using a strap. Because of the small diameter of the tube the strap may not be able to apply much friction to keep the sensor properly positioned, and the sensor may rotate around the tube or move along the tube until the sensor no longer accurately senses the magnet. This effect is especially severe when the tube is tapered and not round. As a result, the rider must periodically adjust the position of the sensor. Another problem with conventional bicycle computers is that the wire from the sensor to the display gives the bicycle a cluttered look, especially when there are other electrical components mounted to the bicycle, each with their own wires.
The present invention is directed to a speed sensor that is integrated with a motor unit used to shift a bicycle transmission. In one embodiment of the present invention, a motor unit is provided for operating an internal hub transmission, and a speed sensor is mounted to the motor unit for detecting a speed signal external to the motor unit. Since the speed sensor is mounted to the motor unit, the position of the speed sensor can be securely fixed on the bicycle. Also, the wire for the speed sensor may be integrated into the wiring harness for the motor, thus eliminating the requirement of a separate wire route along the bicycle.
The motor unit may include an annular housing for receiving a wheel axle therethrough, a drive ring which rotates around a drive ring axis for engaging the hub transmission, and a motor for rotating the drive ring. As a result, the motor unit may be placed in very close proximity to the hub transmission and hence be in very close proximity to the wheel spokes where a signal source such as a magnet is mounted. Because the motor unit can be securely mounted to the bicycle frame, the sensor may be firmly mounted to the housing in a cantilevered manner and extend toward the spokes to be closer to the signal source with less risk of movement than would otherwise be possible.